Synthetic hair color formulations currently on the market typically fall into one of two categories: permanent and semi-permanent.
Permanent hair color formulations consist primarily of oxidative dye systems based on the dual action of two types of precursors—bases (primary intermediates) and modifiers (couplers). Bases are typically aromatic diamines, diaminophenoles, aminophenols, while couplers are typically m-diamines, m-aminophenols and polyphenols (Charles Zviak, The Science of Hair Care, Marcel Dekker Inc., New York, 1986, pp. 265-268; Joseph Rivlin, The Dyeing of Textile Fibers, PCT&S, Philadelphia, 1992, pp. 30-52). The wash fastness of permanent dyes is about 30-40 shampoo cycles. There are, however, a number of issues with permanent dyes. The primary amine used in these oxidative dye systems is generally paraphenilene-diamine (PPD), for which there is growing evidence of and concern over its carcinogenicity and mutagenicity (The Use of Permanent Hair Dyes and Bladder Cancer Risk, SCCNFP/484/01, 2001). Other oxidative dye system precursors, such as the coupler resorcinol, also show toxicity (David Steiman & Samuel Epstein, The Safe Shopper's Bible, Macmillan, 1995, pp. 240-243). The oxidative action of these types of dye systems is provided by hydrogen peroxide at a high pH, which is known to damage hair and irritate the scalp and skin. Most patented developments in the permanent dye area are aimed at decreasing toxicity, hair damage and irritation (J. F. Corbett, Hair Coloring, Clinics in Dermatology, vol. 6, no. 3, 1988, pp. 96-101).
Semi-permanent hair color formulations are those based on the use of coal tar dyes. Coal tar dyes fall into direct, acid, and basic color index categories. The wash fastness of these dyes is about 2-10 shampoo cycles (Charles Zviak, The Science of Hair Care, Marcel Dekker Inc., New York, 1986, pp. 242-261). Recent studies in toxicology and ecology have identified most coal tar dyes, especially direct (as defined by color index) and mono-azo/di-azo (as defined by structure) dyes (the most red and red-orange shades), as carcinogens, teratogens and mutagens (David Steinman & Samuel Epstein, The Safe Shopper's Bible, Macmillan, 1995, pp. 240-243). Acid dyes in particular are known to stain the scalp and skin. Most patented technologies in this area are aimed at decreasing toxicity and irritation, as well as regulating fastness and leveling. Leveling refers to the process of spreading the color from the dye evenly over the hair.
The toxicity of current permanent and semi-permanent synthetic hair color formulations is such that many U.S. physicians do not recommend hair coloring during pregnancy, for people with cancer, or for people at high risk of cancer (David Steinman & Samuel Epstein, The Safe Shopper's Bible, Macmillan, 1995, p. 241).
The main problems with using natural dyes (as opposed to synthetic hair color formulations) to color hair have always been that natural hair dyes produce dull shades of color and have poor wash fastness to shampoo. Natural sources of dyes, such as plants, contain low concentrations of colorants, and the dyes that are recovered from those natural sources are often impure and have poor solubility (H. S. Freeman & A. T. Peters, Colorants for Non-Textile Applications, Elsevier, 2000, pp. 382-453). These problems result in products with long and inconvenient application times for natural hair color technology. Moreover, most natural hair dyes are offered in powder form, which is inconvenient for the user.
There are a number of different natural plant dyes available. Those plant dyes include, but are not limited to, indigo, indigo carmine, alizarine, rubiethyric acid, purpuroxanthin, rubiadin, morindanigrin, munjistin, morindadiol, carotene, crocetin, bixin, canthaxanthin, lycopene, capsanthin, apocarotenal, xanthophyll, curcumin, morin, malclurin, luteolin, apigenin, fukugetin, datiscetin, kaempferol, rhamnocitrin, rhamnethin, zanthorhamnin, Isorhamnetin, Rhamnazin, Quercetin, Rutin, Gossypetin, Butin/Butein, Rottlerin, Chlorophyll A/B, Catechin, Fisetin, Lapachol, Juglone, Alkannin, Alkannan, Deoxysantalin, Atromentin, Awobamin, Carajuirin, Dracorhodin, Berberine, Betanin, Orcein, Xanthone, Naphthalene, Riboflavin, Anthocyanin, Lawsone, emblica extract, alfalfa extract, black tea extract, green tea extract, white tea extract, and red sandalwood. At present, henna (Lawsonia intermis) is the most commonly used natural plant dye for hair. However, due to the poor solubility and low concentration of Lawsone, the pigment in henna, a long application time (as much as several hours) is required to produce a weak, dull shade of color. Moreover, Lawsone “has been examined by SCCNFP . . . (and) . . . its latest opinion on Lawsone . . . (is) Lawsone has genotoxicity/mutagenicity potential in vitro and in vivo and that therefore no safe threshold for Lawsone can be established” (SCCNFP/0798/04, 2004).
Furthermore, natural plant dyes generally lack the color fastness and light fastness of synthetic hair color formulations. Problems with the substantivity of plant-based dyes, which is the affinity that a dye has for a particular fiber, have existed for centuries. Mordanting has long been used as a way to increase substantivity of plant dyes. The mordant's function is to form a complex between a polyvalent metal salt and a dye. The application of a mordant traditionally requires at least two steps, and often includes a pre- or post treatment as well. That is because the reaction between mordants and dyes is virtually instantaneous, making it necessary to apply them separately.
The use of mordants has been limited in recent years, however, because of their generally high toxicity. The most common mordants still in use, although rarely, are chromium salts used in the leather industry. Other mordants include salts of aluminum and copper (Joseph Rivlin, The Dyeing of Textile Fibers, PCT&S, Philadelphia, 1992, p. 30-52; H. S. Freeman & A. T. Peters, Colorants for Non-Textile Applications, Elsevier, 2000, pp. 439-448). There are, however, a number of mineral or metal salts that are capable of acting as a mordant, yet lack the toxicity of chromium salts or other typical mordants. Those mineral or metal salts include, but are not limited to, ferrous gluconate, ferrous aspartate, calcium chloride, calcium gluconate, calcium aspartate, magnesium guconate, magnesium aspartate, magnesium citrate, magnesium palmitate, zinc gluconate, zinc aspartate, and manganese gluconate.
There remains a need for a fast-acting, light fast, wash fast, color fast, natural hair dye formulation which avoids the use of potentially harmful ingredients, and in particular provides bright, intense colors without the use of toxic mordanting agents.